1. Field of the Invention
The present invention relates to a light source apparatus employed in an optical-beam scanning apparatus for use in a writing system, such as a digital copying machine and a laser printer, and including a vertical-cavity surface-emitting light source, an optical-beam scanning apparatus that forms an image at high speed by performing scanning with an optical beam emitted from the light source apparatus, and an image forming apparatus that employs the optical-beam scanning apparatus.
2. Description of the Related Art
With a tandem multi-color image-forming apparatus, in which photosensitive drums for different colors are arranged along a conveying direction of a transfer member, a multiple-color image is formed by superimposing color toner images each formed in a corresponding one of image forming stations on one another while a recording medium is conveyed only once along the image forming stations, which can result in speedup (see Japanese Patent Application Laid-open No. 2002-341273, for example).
Meanwhile, multi-beam scanning apparatuses have been proposed as systems that speed up optical scanning apparatuses. A multi-beam scanning apparatus performs scanning with multiple beams at a time to record a plurality of neighboring lines simultaneously, thereby achieving speedup without increasing the rotation speed of a polygon scanner, which is a deflecting unit.
Japanese Patent Application Laid-open No. 2003-211728 proposes a technique of performing scanning by using a two-dimensional array device (vertical-cavity surface-emitting semiconductor laser (VCSEL) array) to form a plurality of lines simultaneously. Because use of a two-dimensional array device allows to increase the number of light emitting sources to as many as dozens or more, sub-scanning pitch on a photosensitive member can be set to one-nth of recording density. Image recording can be performed with higher definition by configuring a unit of pixels in a matrix of multiple, n×m dots.
Such a two-dimensional array device that includes as many as dozens of light sources is typically housed in a ceramic package or the like that includes a lead frame and directly soldered onto a circuit board. Accordingly, the two-dimensional array device is to be attached for fixation to a support of a light source unit with a circuit board therebetween; however, because the height where the two-dimensional array device is mounted varies due to soldering work, dimensional relationship between the surface of the circuit board and the surface of the package is not fixed. Therefore, the technique of supporting the light source unit with reference to the circuit board surface is disadvantageous in failing to position the two-dimensional array device accurately.
To this end, Japanese Patent Application Laid-open No. 2004-6592 discloses a technique of pressing a package member with a circuit board by resiliently deforming the circuit board so that the package surface is positioned without fail.
Meanwhile, multi-color image-forming apparatuses are becoming increasingly faster year after year and hence finding increased use in digital duplication as on-demand printing systems recently. This places demand on the multi-color image-forming apparatuses to have higher definition image quality.
The use of the two-dimensional array device mentioned earlier allows to set sub-scanning pitch on a photosensitive member to one-nth of recording density. Accordingly, high-definition image quality can be obtained by configuring a unit of pixels in a matrix of multiple, n×m dots.
However, as mentioned earlier, a two-dimensional array device is housed in a package, and the two-dimensional array device and the package to each other with an adhesive such as an epoxy adhesive, which makes it disadvantageously difficult to perform highly-accurate positioning even with use of a jig or the like. In addition, because the two-dimensional array device is directly soldered to a circuit board, positioning the two-dimensional array device relative to the support in the light source unit is disadvantageously difficult.
It is also necessary to continuously assure positioning accuracy relative to a coupling lens, which is to be coupled to the two-dimensional array device, in a unit of several micrometers. Failure to assure this positioning accuracy affects a beam spot diameter and a beam pitch of beams irradiated onto a photosensitive member and disadvantageously degrade image quality by a large degree.
With this regard, the technique described in Japanese Patent Application Laid-open No. 2004-6592 is advantageous in that positioning is performed by bringing the package surface of the two-dimensional array device into contact with the circuit board; however, this technique is disadvantageously less reliable in that forcible deforming of the circuit board can develop component defect, such as detachment of solder from electronic components mounted on the circuit board.